1. Field of the Invention
The present invention relates to a heat pump system for a vehicle and a method of controlling the same, and more particularly, to a heat pump system for a vehicle and a method of controlling the heat pump system, which variably controls only a compressor if the number of revolutions of the compressor is less than upper limit of the number of the maximum revolutions of the compressor and operates an electric heater only when the number of revolutions of the compressor reaches the upper limit of the number of the maximum revolutions of the compressor in order to satisfy a target discharge temperature in a heat pump mode, and which does not operate the compressor just by the number of the maximum revolutions of the compressor but differentiates the upper limit of the number of the maximum revolutions of the compressor according to conditions in the maximum heating mode.
2. Background Art
In general, an air conditioner for a vehicle includes a cooling system for cooling the interior of the vehicle and a heating system for heating the interior of the vehicle. At an evaporator side of a refrigerant cycle, the cooling system converts air into cold air by heat-exchanging the air passing outside an evaporator with refrigerant flowing inside the evaporator so as to cool the interior of the vehicle. At a heater core side of a cooling water cycle, the heating system converts air into warm air by heat-exchanging the air passing outside the heater core with cooling water flowing inside the heater core so as to heat the interior of the vehicle.
In the meantime, differently from the air conditioner for the vehicle, a heat pump system which can selectively carry out cooling and heating by converting a flow direction of refrigerant using one refrigerant cycle has been applied. For instance, the heat pump system includes two heat exchangers: one being an interior heat exchanger mounted inside an air-conditioning case for heat-exchanging with air blown to the interior of the vehicle; and the other one being an exterior heat exchanger for heat-exchanging outside the air-conditioning case, and a direction-adjustable valve for changing a flow direction of refrigerant. Therefore, according to the flow direction of the refrigerant by the direction-adjustable valve, the interior heat exchanger serves as a heat exchanger for cooling when the cooling mode is operated, and serves as a heat exchanger for heating when the heating mode is operated.
Various kinds of the heat pump system for the vehicle have been proposed, and FIG. 1 illustrates a representative example of the heat pump system for the vehicle.
As shown in FIG. 1, the heat pump system for the vehicle includes: a compressor 30 for compressing and discharging refrigerant; a high-pressure side heat exchanger 32 for radiating heat of the refrigerant discharged from the compressor 30; a first expansion valve 34 and a first bypass valve 36 mounted in parallel for selectively passing the refrigerant passing through the high-pressure side heat exchanger 32; an exterior heat exchanger 48 for heat-exchanging the refrigerant passing through the first expansion valve 34 or the first bypass valve 36 outdoors; a low-pressure side heat exchanger 60 for evaporating the refrigerant passing through the exterior heat exchanger 48; an accumulator 62 for dividing the refrigerant passing through the low-pressure side heat exchanger 60 into a gas-phase refrigerant and a liquid-phase refrigerant; an interior heat exchanger 50 for heat-exchanging refrigerant supplied to the low-pressure side heat exchanger 60 with refrigerant returning to the compressor 30; a second expansion valve 56 for selectively expanding the refrigerant supplied to the low-pressure side heat exchanger 60; and a second bypass valve 58 mounted in parallel with the second expansion valve 56 for selectively connecting an outlet side of the exterior heat exchanger 48 and an inlet side of the accumulator 62.
In FIG. 1, the reference numeral 10 designates an air-conditioning case in which the high-pressure side heat exchanger 32 and the low-pressure side heat exchanger 60 are embedded, the reference numeral 12 designates a temperature-adjustable door for controlling a mixed amount of cold air and warm air, and the reference numeral 20 designates a blower mounted at an inlet of the air-conditioning case.
Meanwhile, in order to secure the heating performance, an electric heater (not shown) is mounted inside the air-conditioning case 10.
According to the heat pump system having the above structure, when a heat pump mode (heating mode) is operated, the first bypass valve 36 and the second expansion valve 56 are closed, and the first expansion valve 34 and the second bypass valve 58 are opened. Moreover, the temperature-adjustable door 12 is operated as shown in FIG. 1. Accordingly, the refrigerant discharged from the compressor 30 passes through the high-pressure side heat exchanger 32, the first expansion valve 34, the exterior heat exchanger 48, a high pressure side 52 of the interior heat exchanger 50, the second bypass valve 58, the accumulator 62, and a low pressure side 54 of the interior heat exchanger 50 in order, and then, is returned to the compressor 30. That is, the high-pressure side heat exchanger 32 serves as a heater and the exterior heat exchanger 48 serves as an evaporator.
When an air-conditioning mode (cooling mode) is operated, the first bypass valve 36 and the second expansion valve 56 are opened, and the first expansion valve 34 and the second bypass valve 58 are closed. Furthermore, the temperature-adjustable door 12 closes a passage of the high-pressure side heat exchanger 32. Therefore, the refrigerant discharged from the compressor 30 passes through the high-pressure side heat exchanger 32, the first bypass valve 36, the exterior heat exchanger 48, the high pressure side 52 of the interior heat exchanger 50, the second expansion valve 56, the low-pressure side heat exchanger 60, the accumulator 62, and the low pressure side 54 of the interior heat exchanger 50 in order, and then, is returned to the compressor 30. That is, the low-pressure side heat exchanger 360 serves as an evaporator and the high-pressure side heat exchanger 32 closed by the temperature-adjustable door 12 serves as a heater in the same with the heat pump mode.
However, in order to satisfy a target discharge temperature, the conventional heat pump system for the vehicle variably controls the number of revolutions of the compressor 30 and a heat generation rate of the electric heater at the same time, and hence, the conventional heat pump system for the vehicle has a problem in that convergence of an air discharge temperature in the interior of the vehicle is deteriorated or becomes unstable due to the simultaneous variable control of the number of revolutions of the compressor 30 and the heat generation rate of the electric heater.
Additionally, the conventional heat pump system for the vehicle has another problem in that an operational noise of the compressor 30 is increased because the compressor 30 is operated just at the maximum revolutions in the maximum heating mode and it causes a passenger's dissatisfaction.